Fluids such as water and mixtures of water and methanol have been injected into the induction passages of turbo-charged and other supercharged engines to suppress detonation under high load conditions. Suppression of detonation allows an engine to operate with a charge of higher density and a leaner air-fuel ratio and with more advanced ignition timing than would be possible otherwise.
It will be appreciated, however, that an engine control system that calls for injecting a detonation suppressing fluid into the induction passage--and at the same time calls for increasing the charge density, leaning the air-fuel ratio and advancing the ignition timing--could produce adverse operating conditions if the charge density is increased, the air-fuel ratio is leaned and/or the ignition timing is advanced beyond normal operating ranges even though the fluid is not actually injected into the induction passage.